1. Field of the Invention
The present invention relates to a display device, and more particularly to the connection structure of a terminal portion and the constitution of a flexible wiring film for establishing an electrical connection of a flat display device with an external circuit.
2. Description of the Related Art
The application of a liquid crystal display device has been spreading from computer monitors, mobile phones and the like to television receiver sets. To drive a liquid crystal display panel, it is necessary to supply a power source, signals and the like to the liquid crystal display panel from the outside. The power source, the signals and the like are often supplied by way of a chip-on-film (COF) which is connected to a terminal portion of the liquid crystal display panel. The COF is a film which forms terminals for connection with terminals of the liquid crystal display panel on one side thereof, forms terminals for connection with a printed circuit board or the like on another side thereof which faces the above-mentioned one side thereof in an opposed manner, and mounts an IC chip which incorporates a liquid crystal drive circuit and the like therein on an upper surface thereof. A technique which uses a tape carrier package (TCP) in place of the COF has been also has the same technical background.
The terminals of the COF for connecting the COF with the liquid crystal display panel or the like is large in number and, at the same time, various kinds of COFs have been known. For example, with respect to lines formed on the COF, lines for supplying the power source to the liquid crystal display panel are formed with a width larger than a width of other lines. Corresponding to such widening of the power-source supply lines, the terminals for supplying the power source to the liquid crystal display panel are formed with a size larger than other terminal portions to allow a large current to flow therethrough. On the other hand, the COF and the terminals of the liquid crystal display panel are connected with each other using an anisotropic conductive film. That is, the liquid crystal display panel and the COF are connected with each other by sandwiching the anisotropic conductive film between the terminals of the liquid crystal display panel and the COF and by bonding the terminals of the liquid crystal display panel and the COF by thermocompression bonding.
The thermocompression bonding is performed by pushing a thermal head to the COF from above. In performing such a connection method, when the COF terminals differ in size, width, pitch and the like, a temperature, a pressure or the like applied to the connection portion becomes partially non-uniform thus often damaging the reliability of the terminal portions. To cope with such a drawback, for example, even when the sizes of the terminal portions of the liquid crystal display panel differ from each other, a pitch of the terminal portions of the COF is set smaller than a width of the terminal of the liquid crystal display panel and is set to a uniform value. The anisotropic conductive film becomes conductive in the direction that the liquid crystal display panel and the COF face each other in an opposed manner and becomes non-conductive in the direction perpendicular to such an opposedly facing direction. There has been known a technique which enhances the reliability of the terminal portions by adopting such a constitution.
Further, it is not always the case that all sides of the COF or the liquid crystal display panel have the terminal portions and there are some sides which do not have terminal portions. When some sides do not have the terminal portions, a condition for performing the thermocompression bonding using the thermal head differs and hence, the connection of the terminal portions becomes non-uniform. To prevent such non-uniform connection of the terminal portions, patent document 1 (JP-A-9-260579) describes a technique in which even when a liquid crystal display panel or an IC chip mounted on a COF has a side which does not have terminal portions, a dummy terminal is formed on COF corresponding to a position without a terminal so as to make a connection condition of the terminal portions uniform thus enhancing the reliability of the terminal portions.